1. Field of the Invention
The present invention relates an epoxidation reaction system which uses fixed bed reactors packed with solid epoxidation catalyst.
2. Description of the Prior Art
It is known to produce oxirane compounds such as propylene oxide by catalytic reaction of an olefin with an organic hydroperoxide. See, for example, basic U.S. Pat. No. 3,351,635.
In certain embodiments, fixed bed reactors packed with solid heterogeneous epoxidation catalyst are employed. See, for example, U.S. Pat. Nos. 5,849,937 and 6,365,761.
There are certain problems associated with fixed bed epoxidation systems. On the one hand, high concentrations of organic hydroperoxide reactant cause problems with heat removal and temperature control in the system. Catalyst deactivation rates are accelerated at high temperatures and by feed poisons. Also process selectivity is greatly improved at higher ratios of olefin to hydroperoxide.
However, where high olefin to hydroperoxide ratios are used it is necessary to recover and recirculate large amounts of olefin and this has an adverse effect on process economics.
In addition, it is important that hydroperoxide conversion be essentially complete both for economic and safety reasons.
The present invention provides an improved system and process for oxirane compound production using fixed bed reactors.
In accordance with the present invention, olefin and organic hydroperoxide are passed through two or more fixed bed reactors which are packed with fresh or high activity catalyst, the hydroperoxide being fed in parallel to the reactors and the olefin being fed in series. Thereafter, the reaction effluent from the last of the high activity catalyst reactors is fed through one or more additional fixed bed reactors packed with used, partially deactivated catalyst to complete the reaction.